403 error when accessing the admin section of my website - symfony1

Question

I got a website I inherited. It's been been moved to a new server and now the admin section of the website does not work. I get a 403 when I click on the link.
error message on my browser
Forbidden
You don't have permission to access /admin.php/main/index on this server.
Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.
seems ErrorDocument is a symfony function so I suppose this error has nothing to do with Apache.
In the web folder, there is a admin.php and admin_dev.php.
admin.php
<?php
require_once(dirname(__FILE__).'/../config/ProjectConfiguration.class.php');
$configuration = ProjectConfiguration::getApplicationConfiguration('admin', 'prod', false);
sfContext::createInstance($configuration)->dispatch();
admin_dev.php
<?php
require_once(dirname(__FILE__).'/../config/ProjectConfiguration.class.php');
$configuration = ProjectConfiguration::getApplicationConfiguration('admin', 'dev', true);
sfContext::createInstance($configuration)->dispatch();
As you can see, the only difference is the environment name ("prod" vs "dev" and the last value is for debugging (according to http://www.symfony-project.org/api/1_1/sfProjectConfiguration#method_getapplicationconfiguration).
I copied the contents of admin_dev.php to admin.php. and the refreshed my admin page and the 403 disappeared albeit there is the dev toolbar on top. I changed "dev" to "prod" and leave debugging to on and then refreshed my page again and this time I got the 403.
I looked into the settings.yml and copied the contents of the dev section into the prod section.
But this didn't do anything. Still getting the 403 after refreshing page.
Here's the new contents of settings.yml (you can see the previous settings for prod which I commented out).
settings.yml
# You can find more information about this file on the symfony website:
# http://www.symfony-project.org/reference/1_4/en/04-Settings
# .settings:
# no_script_name: false
# logging_enabled: false
prod:
# .settings:
# no_script_name: false
# logging_enabled: false
.settings:
error_reporting: <?php echo (E_ALL | E_STRICT)."\n" ?>
web_debug: true
cache: false
no_script_name: false
etag: false
dev:
.settings:
error_reporting: <?php echo (E_ALL | E_STRICT)."\n" ?>
web_debug: true
cache: false
no_script_name: false
etag: false
test:
.settings:
error_reporting: <?php echo ((E_ALL | E_STRICT) ^ E_NOTICE)."\n" ?>
cache: false
web_debug: false
no_script_name: false
etag: false
all:
.settings:
# Enable sfGuard
enabled_modules: [default, sfGuardGroup, sfGuardUser, sfGuardPermission, sfGuardAuth]
# Form security secret (CSRF protection)
csrf_secret: 10fee9ab83d0083fb244e5e087afab5fe684cb64
login_module: sfGuardAuth
login_action: signin
secure_module: sfGuardAuth
secure_action: secure
# Output escaping settings
escaping_strategy: true
escaping_method: ESC_SPECIALCHARS
# Enable the database manager
use_database: true
Every time I change a file on the server, I clear my cache via symfony cc.
Any ideas what could be wrong?